The Manufacture, Properties and Uses of Inflated 1985 LENZINGER BERICHTE Heft 58 The Manufacture,...
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Juni 1985 LENZINGER BERICHTE Heft 58
The Manufacture, Properties and Uses of Inflated Viscose Fibres
C. R. Woodings, A. J. Bartholomew, Courtaulds Research, Coventry (UK)
Methods of creating inflated fibres are reviewed, and processes which have been operated commercially are highlighted. The development work on the sodium carbonate route which leads to the cor&nercial large scale production of hollow rayon and the so called super-inflated rayon is described. The lesser known members of the inflated fibre family are mentioned, and their Position in the inflation hierarchy is discussed. The most dramatic effect of the inflation process is the substantial alteration of the fibre shape and surface area, and this is illustrated by a series of scanning electron mlcrographs. Desirable and undeslrable side effects on the other key fibre properties are listed and discussed. The way in which fibre characteristics alter in a predicatable and controllable manner with alterations in production conditions is described. The actual and potential applications of the whole family of products in knitted, woven, non-woven, papermaking, and surglcal products are reviewed. Es werden Verfahren zur Herstellung von gebkihten Fasern be- schrieben und gewerblich eingesetzte Verfahren hervorgeho- ben. Die Entwicklungsarbeit an Natriumkarbonaten, die zurge- werblichen Massenproduktion von hohlem Rayon und soge- nanntem supergeblhtem Rayon fhrte, wird beschrieben. Die weniger bekannten Mitglieder der geblhten Faserfamilie wer- den errtert und ihre Position in der Rangordnung wird bespro- chen. Die drastischste Wirkung des Blhverfahrens ist die nderung der Faserform und des Faseroberflchenbereichs. Dies wird mit mehreren Mikroaufnahmen eines Elektronenmikroskopes dar- gestellt. Wnschenswerte und unerwnschte Nebenwirkungen uf andere wichtige Fasereigenschaften werden aufgefhrt nd besprochen. Es wird die Art beschrieben, in der sich die Faser- merkmale in vorhersehbarer, kontrollierbarer Weise ndern, einschlielich der nderungen in den Produktionsbedingungen. Die derzeitigen noch mglichen Anwendungen der ganzen Pro- duktpalette in Gewirken, Geweben und Vliesstoffen. in der Pa- pierherstellung und in der Herstellung von medizinischen Pro- dukten werden beschrieben.
Introduction Inflated viscose fibres have been known ever since the first viscose fibres were spun at the Start of this century. They appeared from title to time as an annoying ans unmedictable m-oblem of textile varn manufacture. and ha;e even beei known to plague the more modern staple fibre operations. Clearly the fact that we choose to give a Paper on these fibres at a Conference whose theme is Man- made fibres help solvegroblems suggests that their Status has improved in recent years. What has happened to bring about this Change? Without doubt, the persistente of the early researchers who tried to convert a Problem of textile yarn manufacture into a new and marketable fibre was fundamentally important. Furthermore, the major improvements which have occurred in the technology of viscose manufacture, especially in the field of computerised process control, have been an essential element in the development of the stable production processes now used. However, it is probably the
Change in market requirements which has contributed most to the recent growth of interest in and sales of the inflated products.
As you will see, the inflation process tends to make fibres weaker and more extensible in both the dry and wet states, thus amplifying the differentes between these fibres and the Synthetics. Obviously properties such as warmth, comfort, bulk, lightness, covering power, absorbency, purity and others are now regarded as sufficiently important to outweigh not only the traditional disadvantages of viscose fibres but also the additional penalties of inflated production. In the course of this Paper we will review the technology of production of the inflated fibres since their discovery and illustrate how the various types are made and used in todays conventional textile and nonwoven industry.
1. A Review of Inflation Processes The early commercial rayons were intended as substitutes for natura1 silk, although most suffered from the properties of harsh handle, hard metallic-type lustre and lack of cover or insulation, all these properties being uncharacteristic of the true product. To help eliminate some of these Problems attempts were made to produce hollow rayons. Although hollow rayon fibres (straws etc.) were produced as early as 1910 by a hot-pin process, the idea of incorporating an inert gas into the viscose Solution to generate inflated fibres was not patented until 1920 by L. Dr&. J. Rousset developed this idea to include the use of gas generating additives such as metal carbonates or volatile liquids, which develop gas or vapour within the spinning fibres by the action of the acid or the heat from the spin bath3. Courtaulds later patented the idea of producing inflated fibres without added agents, but using a low soda viscose*. These early ideas were improved and developed5 - * but most of the subsequent ideas were simply refinement.s of the two basic processes of emulsification/dissolution and gas generation. One notable exception was the use of electrolysis of the viscose just Prior to spinning to controllably generate Oxygen bubbles within the fibresg. However, this process never became commercial! Other notable developments are listed below: 1925 -- Two bath process. Coagulation and carbonate
impregnation followed by regeneration and inflation.
1926 - Twin gear Pumps, the second running faster than the first, to introduce gas bubbles.
1926 - Use of magnesium sulphate in the spin bath to promote more uniform inflation and more circular Cross-section.
1926 - Vacuum evaporation of a volatile fluid13.
The first commercial inflated fibres evolved in the 1920s under the Celta brand-name. larnelv bv the Alsa Company. Other types were also &ailble, &own by the names of Luftseide and Soie Nouvelle. These early fibres were used to create light yarns with high covering power. The early processes suffered from difficult spinning and from lack of inflation control (a lot of the fibres ended up as flattened tubes and some were not inflated at all). In 1942 Bubblfil was produced by du Pont de Nemours. This process used air injection just Prior to spinning the viscose through very large jet holes to create fi laments with spaced bubbles. The fibre was popular as a buoyancy aid in life jackets, pontoons and rafts during the war. Also it was considered to have good insulating properties and was used for this purpose in aviators uniforms and in sleeping bags. Production stopped in 1943. The development slowed dramatically after the earlg work. In the 1940s several Patents emerged the USA14g They were essentially similar to the earlier reports and were not commercialised. It was not until 1960 that further Patents,
Heft 58 LENZINGER BERICHTE Juni 1985
originating in the USA, were issued relating to the production of flat inflated fibres which were particularly useful for paper-making16. The processes described used the gas emulsion technique, the emulsions being stabilised by the use of surfactants in the viscose. These developments led to the commercial production of RDlOl in the USA by the American Viscose Corporation. Soon after Courtaulds introduced PM1 and PM2 fibres made by a sodium carbonate route17. PM1 fibre was designed for use in high quality Papers. PM2, a slightly less inflated version of PMl, was developed for medical nonwovens, particularly nappies and sanitary towels. At about the same time several Patents by Japanese workers were issued for similar paper-making fibres made by sodium carbonate routes, but also incorporating water swellable chemicals within the fibres18. A lot of work was carried out to determine the important factors for the production of good paper-makins fibres - notably Treiber, Dumbleton and EhrengardlgB . However, substantial markets in these areas never materialised and production of all of these fibre developments has now stopped. Courtaulds continued work on the sodium carbonate route with particular emphasis on controlling the inflation process to produce distinctly different fibre types in 100% form. In 1968 a permanently hollow fibre was developed by using modified viscose and high salt figure (Viloft 21) and later (1969 and 1972) two types of highly inflated and collapsed fibre types were produced using unmodified viscose at low salt figure and spinning into a high temperature, high acid spin bath (SI Fibres 22, 23). In 1984 a product derived from Viloft (Courcel) was introduced in the USA.
progressing from Standard rayon through to super inflated fibre the uncollapsed tube diameter gradually increases and the cellulose wall thickness decreases. The effects tan be seen more clearly in the micrographs.
2.2. The Mechanism of Inflation To understand how these various forms are produced and how the inflation process Comes about, it is probably worth asking in the first instance why all rayon fibres are not inflated. The viscose process generates sodium carbonate and sodium trithiocarbonate by carbon disulphide by- product reactions: 3CSz + 6NaOH + Na,CO, + 2Na,CS, + 3Hz0 These by-products will decompose in the spin bath to give carbon dioxide and hydrogen sulphide. ,By performing calculations including viscose y number, carbon disulphide and cellulose content, it is possible to estimate the amount of these gases which will be liberated in acid. The answer is approximately 3 + 4L for every 1L of viscose (at NTP). This then is more than enough gas to inflate all of the fibres produced, and so why do Standardrayon fibres not contain bubbles? The answer to this question is not entirely certain but i